After 12 years of isolating Iran - operating in that mode has become second nature - what are the benefits, the challenges the US faces, and what happens to this agreement in a post Obama administration given all the partisan naysaying?

"Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning."

Prime Minister Winston Churchill spoke these memorable words to mark the British victory over Nazi Germany in the Battle of Egypt, which marked a momentous turn in the Allied campaign against Hitler. Many years of "blood sweat and tears" remained, but the fortunes of war had turned.

History of Iran-US relations

The deal reached between Iran and the P5+1 also marks a historic turn in the tide of animosity, sanctions, and conflict that have defined the relationship between Iran and the West in the many decades since the Iranian revolution of 1979.

Fragile understandings

The understandings reached these days in Lausanne, like Britain's victory in Egypt's western desert, are fragile. Celebration would be premature.

All parties will be challenged in the coming months and years to reaffirm their commitment, not only to the technical requirements of the agreement on the nuclear file, which is but a way station on the road to rapprochement, but also to reimagine a better relationship between Iran and the West.

While caution is the order of the day, it is also clear that the era of hostility and isolation with the West that commenced with the mullahs' destruction of the pro-US Pahlavi dynasty is now evolving into a more productive and mutually beneficial relationship.

The contours of this new era are only now beginning to take shape, challenging not only Iran but also the US and its allies to reimagine a better more productive sort of engagement on a broad array of economic, cultural as well as security issues.

While caution is the order of the day, it is also clear that the era of hostility and isolation with the West that commenced with the mullahs' destruction of the pro-US Pahlavi dynasty is now evolving into a more productive and mutually beneficial relationship.

The US policy establishment after two sterile generations, is schooling a new breed of diplomats. Their arsenal is no longer limited to weapons, boycott, and rejection.

It also is increasingly one that sees advantage in engaging Tehran in efforts to build a productive diplomatic relationship and that more broadly encourages them to consider how to manage a regional policy that slowly, in fits and starts, aims to recognise and thereby limit legitimate Iranian interests and concerns.

Foundation for the future

These days in Lausanne, the Obama administration, whose diplomatic and military record in creating stable and productive outcomes in the Middle East could hardly be worse, has shown a far different, more committed, imaginative, and successful face.

With Iran, US diplomats are building rather than destroying a foundation for the future. At the very least, a new generation of American diplomats and more broadly American diplomacy has begun to consider how to define Iranian interests, now in the nuclear and economic domains, but also in regional security - from Iraq to Yemen.

This is a welcome and a dramatic development to generations of Americans, who until very recently never saw any interest, professional or otherwise, in challenging the policy of estrangement and boycott. Thankfully, this era is now ending.

Just as no one except for professionals, remembers the technical details of US-Soviet nuclear diplomacy, so too will the detailed understandings on Iran's nuclear programme, now at centre stage, command less attention. In 20 years, who will remember or care about how many of this or that centrifuge Iran possesses or what Iran does with enriched fuel?

Policy and regional security is more about intentions than capabilities. The Obama administration, to its credit, is now taking the first, hesitant step in the direction of constructing a system of relations with Iran that seeks to incorporate both elements of this equation and in so doing enhance the prospects of building security in a region reeling from the destruction of the old order.

Crumbling regional security

Neither Iran, nor Washington, Israel or the Arabs will easily surrender advantages of the crumbling regional security environment that they still enjoy. Israel's prime minister for example warns: "One cannot understand that when forces supported by Iran continue to conquer more ground in Yemen, in Lausanne they are closing their eyes to this aggression. We are not closing our eyes and we will continue to act against every threat."

There will always be those who, for a variety of reasons, prefer to look forward by looking backwards.

This will be Obama's main domestic challenge in the weeks and months ahead, both among his political antagonists in the Republican Party majority in Congress as well as from his nominal allies among the Democrats.

The inherent power of a US president to prevail over Congressional efforts to undermine his Iran initiative gives Obama the advantage. Obama, in search of a foreign policy legacy, will be forced to defend not only his historic decision to engage Iran but also the power of the president to make foreign policy.

The historic decision to engage Iran offers Obama perhaps the best, and last opportunity of his remaining tenure to build a constructive legacy - one that for all of its perils holds the promise of overshadowing grievous errors and shortcomings that have characterised much of his policy in the region during his presidency.

Obama is no Churchill, but a framework agreement with Iran offers sceptical and often hostile critics the uncertain promise of a better future.

Geoffrey Aronson writes about Middle East affairs. He consults with a variety of public and private institutions dealing with regional political, security, and development issues.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.